This blog is intended as an occasional diary of information to feed back to hoverfly recorders in the UK and elsewhere. Inevitably there will be issues of interest that are in some way relevant to invertebrate ecologists and consequently I intend to use the medium as an opportunity to develop thoughts on pertinent topics.

Tuesday, 23 December 2014

In a few moments of inactivity I took a look at the
phenology of a few species seen this year. One that I thought worth looking at
was Episyrphus balteatus as it is reported in very large numbers. The attached
histograms are strictly for photographic records - I will look in more detail
once the garden records have arrived.

Data were plotted in four blocks:

All records for 2014 and 2013 plotted separately

South of a line created by the northern limits of ST/SU/TQ plotted as separate years 2014 and 2013.

Midlands - up from the northern limits of ST/SU/TQ to the
southern limits of SE/SD plotted as separate years 2014 and 2013.

North - north of the limits of the southern limits of SE-SD plotted as separate years 2014 and 2013.

The results were a bit of a surprise:

It looks as though there might be as many as four generations
in southern England - I expected 3 but there is a bit of a March
generation too.

In 2014 I found no migration peak at the end of July but there
is quite a spike by late June - and a pronounced spike in the
Midlands.

The number of generations in the midlands is a bit messy -
probably 3, but I cannot be sure. It begs the question - can one
come up with a series of thermoclines to come up with
differences in phenology?

The northern population seems to have a distinct single
generation.

What I think it starts to tell us is that
every year is very different, and that this species probably has slightly different
emergence strategies even between southern England and the Midlands. In 2014,
in which we had an exceptionally mild spring and autumn it looks as though
there were probably at least 4 generations in southern England, whereas the
further north one gets it seems to be broadly univoltine.What I find particularly puzzling is that the late July
migration spike was not picked up this year. I have a feeling
that this may only be detected by absolute counts.

About Me

An ecologist with over 30 years experience in statutory nature conservation and biological recording. I am now an independent coastal management consultant (Bright Angel Coastal Consultants Ltd.) and have undertaken commissions in the UK and several northern European countries. I originally trained as an entomologist and parasitologist. Today, I retain an interest in entomology but in a strictly non-vocational capacity. In my non-working time I am joint organiser of the Hoverfly Recording Scheme (with Dr Stuart Ball) and am extremely committed to developing new capacity in insect identification and biological recording.